Many articles that are employed in the aerospace industry, such as nozzles for rocket engines, are subjected to extremely high temperatures which would cause the article to fail if the article were not actively cooled. One technique for actively cooling such articles includes the use of one or more tubes that are stacked on one another to at least partially form a wall of the article. When the article is in use, a coolant is pumped through the tubes to cool the article and prevent its failure despite the exposure to highly elevated temperatures.
Current manufacturing techniques employ highly toleranced tubes which are fit closely together during the fabrication of the article and thereafter brazed together. Often times, the dimensions of the tubes are painstakenly measured and match-fit into gaps to obtain the best possible fit. Despite these efforts, gaps between the tubes are inevitable and an additional amount of braze alloy (in the form of a paste) is placed between the tubes. Despite the use of additional braze alloy, these gaps frequently result in tube-to-tube braze voids that are found after the brazing operation has been completed. As these tube-to-tube braze voids negatively affect the heat transfer of the article, the article must be laboriously inspected and repaired. The repair consists of filling the tube-to-tube braze voids with additional braze alloy and re-brazing the entire article. Thereafter, the article is re-inspected to identify the presence of tube-to-tube braze voids. Additional brazing and inspecting cycles may be necessary if tube-to-tube braze voids are found.
In view of the above, there remains a need in the art for an improved method for forming a tube-walled article. The improved method ideally permits relatively low-toleranced tubes to be employed to reduce the cost of the article as compared to articles formed with highly-toleranced tubes. The improved method also deforms the tubes so as to eliminate the presence of voids, both on the inner and outer sides of the tube, as well as between tubes.